Effects of undernutrition in early pregnancy on systemic small artery function in late-gestation fetal sheep

The aim of this study was to investigate functional development of small arteries from the skeletal circulation of fetal sheep and to determine whether maternal undernutrition affects responses to vasoconstrictive and vasodilatory agonists in arteries from the late-gestation fetus.

We investigated vasoconstrictive and vasodilatory responses of isolated small (approximately 300 microm) arteries from the femoral vascular bed of fetal sheep and from late-gestation pregnant ewes. Ewes were fed either 100% of the nutritional requirement throughout pregnancy (control group) or a restricted diet of 85% or 50% of the nutritional requirement for the first 70 days of pregnancy. For the remainder of pregnancy all ewes were fed the complete diet.

Among control group animals vasoconstriction in response to norepinephrine was well developed in fetuses at 0.6 and 0.9 gestation with respect to that in the ewes. When expressed as a percentage of the response to 125-mmol/L potassium (to correct for differences in vessel size and muscle mass), maximum constriction in response to norepinephrine was greater in fetal vessels from 0.9 gestation than in either those at 0.6 gestation or those of the ewes. Endothelium-dependent vasorelaxation responses to acetylcholine and bradykinin were also well developed in fetuses at 0.6 and 0.9 gestation and were similar to those in the ewes. In fetuses at 0.9 gestation the 50% nutritional restriction of the ewe led to blunted endothelium-dependent vasodilatation in response to acetylcholine and blunted endothelium-independent vasodilatation in response to sodium nitroprusside. Responses in the fetuses at 0.9 gestation in which the ewes were fed a restricted diet of 85% were normal.

This study shows that from midgestation onward small arteries from the skeletal circulation of the fetal sheep have the functional capacity to respond to norepinephrine and endothelium-dependent vasodilators (eg, acetylcholine and bradykinin). The blunted responses to acetylcholine and sodium nitroprusside in the fetuses at 0.9 gestation among the group of dietarily restricted ewes (restricted diet of 50% group) were indicative of impaired vascular smooth muscle sensitivity to nitric oxide. This defect may contribute to the development of hypertension in later life.